The present invention relates to converting DC (direct current) to RF (radio frequency), and more particularly, using a monolithic optical switch to impulse excite a monolithic resonator.
It is known to use an optical switch coupled to a DC supply in order to inexpensively generate high power microwave and millimeter wave signals. Indeed, above about 200 GHz such an arrangement is probably the only practical way of generating signals, except possibly for mixing the signals from two lasers together and selecting the difference frequency signal, since about 200 GHz is the limit for conventional oscillators. In particular, such an arrangement provides such high sub-millimeter wave signals due to the very fast switching time, e.g., one picosecond or less, of the optical switch, which results in harmonics in the sub-millimeter range.
Such arrangements are shown in the articles "High-Frequency Waveform Generation Using Optoelectronic Switching in Silicon" by M. M. Proud, Jr. and S. L. Norman, I.E.E.E. Trans. Microwave Theory Tech., MTT-26, pp. 137-140, 1978, and "Direct DC to RF Conversion by Picosecond Optoelectronic Switching", by C. S. Chang et al., IEEE MTT-S International Microwave Symposium Digest, 1984, pp. 540-541, wherein the optical switch comprises bulk silicon and the later article shows a resonator comprising a cavity, which is bulky. Further, the bulk silicon or other semiconductor must have a high OFF resistance in order to withstand the applied high DC voltage. However, it is then difficult to make a good ohmic contact to the bulk silicon resulting in a high ON resistance, and therefore low efficiency and eventual burn out of the switch due to the heat dissipation thereof. One can make such an arrangement in monolithic form to reduce the size thereof, but the other above-mentioned problems remain. Further, it is normally desirable to have a plurality of such arrangements in monolithic form in order to, e.g., form a phased array. It has been found that using a bulk semiconductor optical switch causes unwanted coupling between the DC to RF converters and interference to the optically triggered timing thereof.
It is, therefore, desirable to have a DC to RF converter that is efficient, reliable, and a plurality of which can be made in monolithic form without undesired coupling therebetween.